Abstarct: In this thesis, the properties and applications of titanium dioxide and doped polypyrrole, as well as their composite, were investigated. Titanium dioxide was synthesized as the baxse material via the sol–gel method, while chlorine-doped (Cl⁻) polypyrrole (PPy) was prepared through chemical polymerization. Subsequently, PPy was employed as a conductive and supporting phase for TiO₂ to enhance charge transfer, reduce electron–hole recombination, and facilitate catalyst separation from the solution after the photocatalytic reaction. Six samples of TiO₂@PPy nanocomposites with various pyrrole concentrations (0–1.5 mol%) were synthesized through in-situ oxidative polymerization. X-ray diffraction (XRD) analysis confirmed the formation of anatase-phase TiO₂ with a tetragonal structure, while photoluminescence (PL) measurements verified the suppression of electron–hole recombination in the presence of PPy. Electrical characterization revealed that anatase-phase TiO₂ exhibits n-type semiconducting behavior. The diode-like I–V characteristics and the significant current flow under forward bias indicate high electron mobility and the presence of oxygen vacancies acting as donor centers. These features play a crucial role in improving photocatalytic performance, gas sensing, and solar cell applications. The photocatalytic performance of the samples was evaluated by degrading methylene blue (MB) dye under low-intensity UV irradiation. The results demonstrated that chlorine doping converted the polymer structure from amorphous to semi-crystalline, and the addition of 1.25 mol% Cl-doped PPy to TiO₂ significantly enhanced photocatalytic activity. The optimized sample degraded 58.5% of methylene blue within 30 minutes—23.5% higher than pure TiO₂—and achieved 96% degradation after 120 minutes, while pure TiO₂ required 180 minutes for the same efficiency. These findings clearly demonstrate that the synergistic interaction between TiO₂ and PPy enhances photocatalytic activity by introducing mid-gap energy states, improving electron–hole pair separation, and facilitating photoinduced charge transfer.